1. Field of the Invention
The present invention relates to a disk player which plays a recorded disk such as a video disk on which a composite video signal (hereinafter simply referred to as video signals) is recorded.
2. Description of the Related Art
A conventional disk player is shown in FIG. 1. In the Figure, disk 1 is rotationally driven by a spindle motor 2. On the disk 1 a video signal is recorded in which a pulse train signal is inserted in a portion corresponding to a predetermined horizontal period in a vertical blanking period. The pulse train signal is obtained by modulating a disk code comprising a time code and a frame number which expresses a position of an information signal recorded on a disk 1. The modulation method, for example, a biphase mark modulation method in which the instantaneous level of the pulse train signal is adjusted to be between the white level and the pedestal level of the video signal.
The information signal recorded on the video disk 1 is read by a pickup 3 with the revolutions of the disk 1. The pickup 3 is held with a slider (not shown in the drawing) which is moved in the radial direction of a turn table by a slider motor 4, and an information detection point (a reading light spot in the case of an optical system) of the pickup 3 can be freely positioned in the radial direction of the disk 1. There are provided a spindle servo system, a tangential servo system, a tracking servo system, a slider servo system, etc., but they are not shown in the drawings because they are well known in the art.
The spindle motor 2 and the slider motor 4 are driven by the spindle servo system, the slider servo system or a play section control circuit 5. The play section control circuit 5 executes the driving of the spindle motor 2 and the slider motor 4, the ON-OFF control for the servo systems described in the above, which are not shown in the drawings, and a jump operation control, etc. in response to commands from the system controller 7.
A so called RF signal output from the pickup 3 is supplied through an RF amplifier 8 to a demodulation circuit 9 which is constituted with an FM demodulator, etc. and produces the video signal. The video signal is supplied to a signal-separation circuit 10 and a video output terminal OUT. The signal separation circuit 10 is constituted to extract a horizontal synchronizing signal h and a vertical synchronizing signal v from a signal obtained by slicing the video signal, for example, at a first fixed level between a pedestal level and a synch-tip level, and to produce a pulse train signal c obtained by slicing the video signal at a second fixed level between a white level and the pedestal level.
The horizontal synchronizing signal h, the vertical synchronizing signal v and the pulse train signal c are supplied to a decoder 11. For example, clock pulses check ck1 of 3 MHz for the demodulation process of the pulse train signal c are supplied to the decodor 11 from a pulse generation circuit 12 comprising a crystal oscillator etc. The decoder 11 is constituted to detect a portion corresponding to a disk code in the pulse train signal c by a horizontal synchronizing signal h and a vertical synchronizing signal v, and successively holds instantaneous levels at the time of generation of the clock pulses ck1 in the portion corresponding to the disk code as bit values of individual bits of the disk code modulated with the biphase mark modulation method, and a disk code is obtained by a decoding process of an obtained bit train.
The disk code demodulated by the decoder 11 is supplied to the system controller 7. The system controller 7 is constituted with a microcomputer comprising, for example, a processor, a ROM, a RAM, etc., and it performs computing operation based on the data and the program stored in the RAM or the ROM following a command corresponding to the key operation supplied from a control section 13, and after that it sends out a command signal such as a play command, a jump command, etc. to the play section control circuit 5.
In the above arrangement, the time duration of a portion corresponding to a bit of a disk code modulated by the biphase mark modulation method in the pulse train signal c supplied to the decoder 11 varies in correspondence to the number of revolution of the disk 1, but the frequency of the clock pulses ck1 is fixed. Therefore, in the decoder 11 unless the number of revolution of the disk 1 becomes close to the rated number of revolutions, the bit value of each bit of the disk code modulated with the biphase mark modulation method is not maintained at a correct value, and the disk code is not demodulated accurately. When, therefore, a search operation is performed, the operation of a processor in the system controller 7 is as follows: at first the processor calculates the number of tracks between the position of the information detection point and the designated position (step S1); and the processor moves the information detection point of the pickup 3 by the number of tracks obtained in the step S1 in driving the slider motor 4, as seen from FIG. 3. After that, the processor repeats the judgements if the number of revolution of the disk 1 is close to the rated number of revolutions (step S3), and only when the number of revolution of the disk 1 is judged to be close to the rated number of revolutions, it takes in the output data of the decoder 11 (step S4) and judges if the position of the information detection point of the pickup 3 coincides with the designated position (step S5). In the step S5, when the position of the information detection point of the pickup 3 is judged to coincide with the designated position, the processor resumes the execution of a routine work being executed just before it moves to the step S1. When the position of the information detection point of the pickup 3 is judged not to coincide with the designated position, the processor performs return to step S1.
As mentioned in the above in the conventional device, after a track-jump the number of revolutions of the disk 1 has to be detected by the process shown in step S3 if it is close to the rated number of revolutions and if it is the output data of the decoder 11 is taken in for judging if the position of the information detection point of the pickup 3 is reached at a designated position. Therefore, in a conventional device, especially in the case of a CLV (constant line speed) disk player in which the rated number of revolutions differs with the position of the information detection point of the pickup 3, a long time is needed after a track-jump till the number of revolutions of the disk 1 reaches at a value close to the rated number of revolutions. It is a drawback to a conventional device that a long time is needed for the completion of a search operation.